The present invention relates to equipment and methods for testing the electrical integrity of electrical circuits, and more particularly to equipment and methods for the non-contact electrical testing of printed circuit boards (xe2x80x9cPCBsxe2x80x9d), chip carriers and similar electrical circuits having conductors of various configurations.
Electrical circuits, such as PCBs and chip carriers, are generally tested after manufacture to determine whether or not all of the conductors and other electrically conductive elements in the circuit are in their designated positions and to ensure that they are not unintentionally cut, shorted or otherwise have an undesired continuity or lack thereof. The conductors of electrical circuits are normally interconnected to define nets.
Conventional methods and apparatus for electrically testing electrical circuits typically employ some kind of physical contact with the nets. For example, in moving probe apparatus, a pair of probes may be physically moved by an X-Y mechanism into and out of contact with terminals of various nets. Because nets are tested sequentially by moving the probes from net to net, moving probe testing is a relatively slow method for electrically testing complicated electrical circuits.
Another method for electrically testing electrical circuits employs a so-called xe2x80x9cbed-of-nailsxe2x80x9d testing fixture. A bed-of-nails fixture typically includes a large number of pins, which are positioned so that when a circuit to be tested is pressed thereagainst, the pins come into electrical contact with pads at the terminal ends of each net to establish electrical contact therewith. The conductivity of each net is subsequently measured. Although an electrical circuit can be tested much faster on an existing bed-of-nails fixture than by using a moving probe, bed-of-nails testing requires a dedicated fixture to be constructed for each electrical circuit configuration. As a result, bed-of-nails testing is, overall, a time consuming and costly solution.
Electrical testing methods which rely on physical contact with an electrical circuit to be tested, such as the moving probe and bed-of-nails methods described above, suffer from at least two additional fundamental disadvantages: First, as the size of pads at the terminal ends of conductors on electrical circuits decreases and their density increases, it becomes increasingly difficult to obtain adequate electrical contact therewith. Second, physical contact between conductor pads and the probes or pins may damage the pads.
To overcome these difficulties, a number of non-contact electrical testing methods have been proposed. One non-contact printed circuit board testing method is described in U.S. Pat. No. 5,218,294, issued to Soiferman. The patent describes stimulating a PCB under test with an AC signal through power and ground lines or layers, or in a non-contact manner by employing a near-field active antenna. The resulting stimulation generates an electromagnetic field which characterizes the PCB under test. The electromagnetic field proximate to the PCB under test is measured in a non-contact manner and compared to the electromagnetic field of a known faultless circuit board to determine whether the PCB under test is defective.
U.S. Pat. No. 5,517,110, also issued to Soiferman, describes non-contact stimulation of a PCB by a pair of stimulators located adjacent to the PCB on one side thereof. A resulting electromagnetic field is detected using a sensor array located between the stimulators on the same side of the PCB.
U.S. Pat. No. 5,424,633, issued to Soiferman describes a spiral loop antenna useful in the electrical testing of PCBs, as well as electrical testing in which an electromagnetic field is applied to a first side of a PCB under test by a non contact stimulator and an array of non-contact sensors on an opposite side of the PCB is operative to measure an electromagnetic field that is characteristic of the PCB when stimulation is applied. This system is able to electrically test nets that have terminal points on opposite sides of a PCB and relatively thin PCBs that do not have internal metal layers.
The present invention seeks to provide improved methods and apparatus for non-contact electrical testing of electrical circuits such as PCBs. For the purpose of the description and claims which follow, an electrical circuit being tested is referred to as a xe2x80x9cboard under testxe2x80x9d or xe2x80x9cBUTxe2x80x9d.
One aspect of a preferred embodiment of the present invention provides for the non-contact electrical testing of BUTs, such as PCBs, that have nets which begin and terminate on the same side thereof, and that have other nets which begin and terminate on opposite sides thereof.
Another aspect of a preferred embodiment of the present invention provides for the non-contact electrical testing of BUTs, such as PCBs, that have internal metal layers and conductors that cross through or between the metal layers.
In accordance with a preferred embodiment of the invention, non-contact electrical testing of BUTs, such as PCBs, that have nets which begin and terminate on the same side as well as nets which begin and terminate on opposite sides is performed generally simultaneously. One side of a BUT is stimulated with an AC electric field at a first frequency and the other side of the BUT is stimulated with an AC electric field at a second frequency. Potentials induced by the different frequency stimulation in conductors on the BUT are measured and separated according to frequency.
It is readily appreciated that by applying stimulation to both sides of the BUT that results in separable potentials that are identified with stimulation applied to one side or the other of BUT, the electric continuity in different types of conductors on a BUT can be tested simultaneously.
In accordance with a still further aspect of the present invention, a pattern of potentials on a BUT is analyzed and compared to a pattern characteristic of an electrical circuit known to be not defective.
There is thus provided in accordance with a preferred embodiment of the present invention an apparatus for electrical testing of an electrical circuit having first and second side surfaces and including a plurality of conductors, the apparatus including at least one stimulation electrode disposed adjacent at least one of the first and second side surfaces of the electrical circuit and being operative to apply thereto a stimulation electromagnetic field in a non-contact manner, at least one sensing electrode disposed adjacent at least one of the first and second side surfaces of the electrical circuit and being operative to sense a resulting electromagnetic field produced by application of the stimulation electromagnetic field at various locations thereon in a non-contact manner, wherein at least one of the at least one stimulation electrode and the at least one sensing electrode includes at least two electrodes at least one of which is disposed adjacent each of the first and second side surfaces of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention the at least one stimulation electrode includes at least first and second stimulation electrodes disposed adjacent respective ones of the first and second side surfaces of the electrical circuit.
Still further in accordance with a preferred embodiment of the present invention the at least one sensing electrode includes at least first and second sensing electrodes disposed adjacent respective ones of the first and second side surfaces of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention there is provided at least one stimulation signal generator providing at least one stimulation signal to the at least one stimulation electrode.
Additionally in accordance with a preferred embodiment of the present invention the at least one stimulation signal generator provides stimulation signals to a plurality of stimulation electrodes in a manner such that signals induced in the electrical circuit by individual ones of the stimulation electrodes may be distinguished from each other, and preferably also includes at least one separating detector for receiving from the at least one sensing electrode signals induced in the electrical circuit by individual ones of the stimulation electrodes and distinguishes the signals from each other.
Additionally the apparatus for electrical testing of an electrical circuit also includes a signal analyzer operative to analyze at least one signal received from the at least one sensing electrode and a comparator receiving at least one signal derived from the resulting electromagnetic field and operative to compare the at least one signal with a reference.
Preferably the apparatus for electrical testing of an electrical circuit also includes a defect report generator providing a defect report relating to the electrical circuit based on the output of the comparator.
Additionally in accordance with a preferred embodiment of the present invention the at least one stimulation electrode includes first and second stimulation electrodes arranged to be disposed alongside a first side of the electrical circuit and a third stimulation electrode arranged to be disposed alongside a second side of the electrical circuit. Preferably the at least one sensing electrode includes a linear array of sensing electrodes.
Still further in accordance with a preferred embodiment of the present invention the linear array is disposed intermediate the first and second stimulation electrodes.
Additionally or alternatively the at least one stimulation electrode includes a linear array of stimulation electrodes.
Preferably the at least one sensing electrode includes first and second sensing electrodes arranged to be disposed alongside a first side of the electrical circuit and a third sensing electrode arranged to be disposed alongside a second side of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention the at least one sensing electrode includes first and second sensing electrodes arranged to be disposed alongside a first side of the electrical circuit.
Still further in accordance with a preferred embodiment of the present invention the linear array is disposed intermediate the first and second stimulation electrodes.
Moreover in accordance with a preferred embodiment of the present invention the at least one signal generator provides signals having different frequencies to different ones of the stimulation electrodes, and the at least one signal generator provides multiplexed signals to different ones of the stimulation electrodes.
Preferably the at least one stimulation electrode includes a plurality of individually controllable sections.
There is also provided in accordance with a preferred embodiment of the present invention a method for electrical testing of an electrical circuit having first and second side surfaces and including a plurality of conductors, the method including the steps of applying an electromagnetic field in a non-contact manner to at least one of first and second side surfaces of the electrical circuit and sensing a resulting electromagnetic field in a non-contact manner at various locations along at least one of the first and second side surfaces of the electrical circuit, wherein at least one of the applying and sensing steps employs non-contact electrodes disposed along both the first and second side surfaces of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention the applying step includes employing at least first and second stimulation electrodes disposed adjacent respective ones of the first and second side surfaces of the electrical circuit to apply at least one electromagnetic field thereto.
Preferably the sensing step includes employing at least first and second sensing electrodes disposed adjacent respective ones of the first and second side surfaces of the electrical circuit to sense the resulting electromagnetic field.
Still further in accordance with a preferred embodiment of the present invention at least one stimulation signal and is generated and provided to at least one stimulation electrode.
Additionally in accordance with a preferred embodiment of the present invention the generating step includes providing stimulation signals to a plurality of stimulation electrodes in a manner such that signals induced in the electrical circuit by individual ones of the stimulation electrodes may be distinguished from each other. Additionally or alternatively the method also includes receiving signals induced in the electrical circuit by individual stimulation electrodes and distinguishing the signals from each other.
Preferably the method electrical testing of an electrical circuit also includes analyzing at least one signal induced in the electrical circuit.
Moreover according to a preferred embodiment, the present invention also includes receiving at least one signal derived from the resulting electromagnetic field and comparing the at least one signal with a reference. Preferably the step also includes providing a defect report relating to the electrical circuit based on the comparing step.
Additionally according to a preferred embodiment of the present invention the applying step employs first and second stimulation electrodes disposed alongside a first side of the electrical circuit and a third stimulation electrode disposed alongside a second side of the electrical circuit.
Still further according to a preferred embodiment of the present invention the sensing step employs a linear array of sensing electrodes. The linear array may also be disposed intermediate first and second stimulation electrodes.
Additionally according to a preferred embodiment of the present invention the applying step employs a linear array of stimulation electrodes. Furthermore the linear array is disposed intermediate first and second stimulation electrodes.
Preferably the sensing step employs first and second sensing electrodes disposed alongside a first side of the electrical circuit and a third sensing electrode disposed alongside a second side of the electrical circuit. Additionally or alternatively the sensing step employs first and second sensing electrodes disposed alongside a first side of the electrical circuit.
Preferably the method for electrical testing of an electrical circuit includes a generating step in which signals having different frequencies are provided to different ones of the stimulation electrodes. Additionally or alternatively the generating step includes providing multiplexed signals to different ones of the stimulation electrodes.
Still further in accordance with a preferred embodiment of the present invention the applying step employs at least one stimulation electrode including a plurality of individually controllable sections.
Additionally according to a preferred embodiment of the present invention also includes the step of grounding an intermediate metal layer in the electrical circuit.
Moreover in accordance with a preferred embodiment of the present invention the sensing step includes sensing potentials on one side of the electrical circuit and sensing potentials on the opposite side of the electrical circuit.
There is also provided in accordance with yet another preferred embodiment of the present invention a method for electrical testing of a multi-layered electrical circuit having first and second side surfaces and including a plurality of conductors, the method including the steps of grounding an intermediate metal layer in the electrical circuit, inducing potentials into at least some of the conductors of the electrical circuit, and sensing a resulting electromagnetic field in a non-contact manner at various locations along at least the first side surface thereof to obtain electromagnetic field data characteristic of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention also includes sensing a resulting electromagnetic field at various locations along at least the second side surface thereof to obtain electromagnetic field data characteristic of the electrical circuit.
Still further in accordance with a preferred embodiment of the present invention the electromagnetic field data is for the potential in conductors including the electrical circuit. Furthermore, the inducing step may include inducing potentials on both a first side and a second side of the electrical circuit.
Additionally in accordance with a preferred embodiment of the present invention the inducing step includes inducing potentials on the first side of the electrical circuit which are differentiable from potentials induced on the second side of the circuit.
Moreover in accordance with a preferred embodiment of the present invention the inducing step includes inducing potentials which are differentiable by frequency.
Still further in accordance with a preferred embodiment, the present invention provides a method for electrical testing of a multi-layered electrical circuit wherein the inducing step includes inducing potentials which are multiplexed.
Moreover in accordance with a preferred embodiment of the present invention the sensing step includes sensing electromagnetic field data on one side of the electrical circuit. Preferably the sensing step further includes distinguishing the electromagnetic field resulting from potentials induced on the first side of the electrical circuit from the electromagnetic field resulting from potentials induced on the second side of the electrical circuit.
Further in accordance with a preferred embodiment of the present invention the inducing step includes inducing potentials on a first side of the electrical circuit.
Additionally or alternatively the inducing step employs a plurality of stimulators, and each stimulator induces potentials which are differentiable by frequency. Preferably the inducing step employs a plurality of stimulators, and each stimulator induces potentials which are multiplexed.
Additionally in accordance with a preferred embodiment of the present invention the sensing step employs at least a first sensor and a second sensor arranged along a first side of the electrical circuit. Preferably the sensing step additionally employs a third sensor located along a second side of the electrical circuit.
Moreover in accordance with a preferred embodiment of the present invention also includes correlating electromagnetic field data sensed by the sensors to a stimulator. Additionally or alternatively a preferred embodiment of the present invention also includes determining electrical continuity of at least some of the conductors by comparing the electromagnetic field data to reference electromagnetic field data characteristic of a desired electrical circuit.
Still further in accordance with a preferred embodiment of the present invention the inducing step is carried out in a non-contact manner.
There is further provided in accordance with a preferred embodiment of the present invention a method for electrical testing of a multi-layered electrical circuit having first and second side surfaces and including a plurality of conductors, the method including the steps of stimulating the electric circuit to induce in proximity thereto an electromagnetic field, acquiring electromagnetic field data in a non-contact manner at various locations along the first side surface, acquiring electromagnetic field data in a non-contact manner at various locations along the second side surface, and determining electrical continuity characteristics of the conductors by analysis of electromagnetic field data for the first side surface and by analysis of electromagnetic field data for the second side surface.
Preferably in the method for electrical testing of a preferred embodiment of the present invention, the analysis steps employs reference data which is characteristic of an electrical circuit having known structure.
Still further in accordance with a preferred embodiment of the present invention the electrical circuit is a multi-layered circuit which includes at least one intermediate layer which is substantially completely metalized, and the method includes grounding the at least one substantially completely metalized layer.
There is further provided in accordance with a preferred embodiment of the present invention a method for electrical testing of an electrical circuit having a plurality of electrically conductive elements, the method including the steps of applying a first electromagnetic field to the electrical circuit with at least one stimulator located near but not contacting the article on a first side thereof, applying a second electromagnetic field to the article at generally the same time as the first electromagnetic field with at least one stimulator located near but not contacting the article on a second side thereof, and separately detecting first and second potentials induced on the electrically conductive elements of the article by the first and second electromagnetic fields, respectively.
Further in accordance with a preferred embodiment of the present invention the first and second steps of applying an electromagnetic field include the steps of generating electromagnetic signals of first and second frequencies, respectively.
Still further in accordance with a preferred embodiment of the present invention the step of separately detecting includes the step of sensing the potentials with at least one sensor located near the first side of the article. Preferably the method further includes the step of scanning by at least one sensor.
Additionally according to a preferred embodiment of the present invention the step of scanning includes the step of scanning in a first scanning direction and followed by the step of scanning in a second scanning direction which is substantially perpendicular to the first scanning direction. Additionally or alternatively the step of scanning includes the step of scanning the article in a first position followed by the step of scanning the article in a second position which is upside-down from the first position.
Preferably the method further including step of grounding internal metal layers of the article.
There is also provided in accordance with a preferred embodiment of the present invention an apparatus for electrically testing an article having an electric circuit therein formed of a plurality of conductors, in which the apparatus includes (i) a first electromagnetic field generator applying a first electromagnetic field to the article, wherein the first field generator includes at least one stimulator located near but not in contact with a first side of the article, and (ii) a second electromagnetic field generator applying a second electromagnetic field to the article, wherein the second field generator includes at least one stimulator located near but not in contact with a second side of the article, wherein the second side is opposite the first side, and (iii) a sensor operative to separately detect first and second potentials induced on the conductors by the first and second electromagnetic fields, respectively.
Further in accordance with a preferred embodiment of the present invention the sensor includes an array of sensors adjacent to the at least one stimulator of the first field generator. Preferably the first field generator generates an electromagnetic field at a first frequency, and the second field generator generates an electromagnetic field at a second frequency. Additionally or alternatively in the apparatus for electrically testing an article, the first field generator includes a first stimulator and a second stimulator operative to generate the electromagnetic field.
Additionally according to a preferred embodiment of the present invention the first stimulator and second stimulator each generate a field which are 180 degrees out of phase with respect to each other. Preferably the stimulators are made of a plurality of strip-shaped elements.
Still further in accordance with a preferred embodiment of the present invention the strip-shaped elements extend obliquely relative to the array of sensors.
Additionally or alternatively at least one of the stimulators is made of a plurality of patch-shaped stimulators.
There is also provided in accordance with a preferred embodiment of the present invention a method for electrically testing an article having a plurality of conductors therein, which preferably includes the steps of subjecting a first side of the article to an electromagnetic field with at least one stimulator in close but not in contact arrangement with a first side of the article, scanning the side of the article in at least two partially orthogonal directions with a not in contact sensor, sensing potentials induced on the conductors by the electromagnetic field, and analyzing the potentials to determine the existence of defects in the elements.
Still further in accordance with a preferred embodiment of the present invention the method also includes the additional steps of subjecting a second side of the article to a second electromagnetic field with a second stimulator in close but not in contact arrangement with the second side, scanning the side of the article in at least two at least partially orthogonal directions with a not in contact sensor and sensing the induction of potentials induced on the elements by the second electromagnetic field, and analyzing the potentials induced by the second electromagnetic field to determine the existence of defects in the elements.
Additionally according to a preferred embodiment of the present invention the article is subjected to the first and second electromagnetic fields at generally the same time. Preferably the electromagnetic fields are propagated at different frequencies. Additionally or alternatively the article includes a metal layer, and the metal layer is grounded.
Moreover according to a preferred embodiment of the present invention the article is subjected to the first and second electromagnetic fields one after the other.
There is also provided in accordance with a preferred embodiment of the present invention a method for the electrical testing of an article having a plurality of electrically conductive elements and internal conductive layers, the method including the steps of subjecting the article to an electromagnetic field with at least one stimulator in close but not in contact arrangement with at least one side of the article, grounding the internal conductive layers of the article, scanning the at least one side of the article with a not in contact sensor and sensing the induction of potentials induced on the elements by the electromagnetic field, and analyzing the potentials to determine the existence of defects in the elements.